The invention relates to a tomographic apparatus for producing transverse layer images of a radiographic subject, with an x-ray measuring arrangement containing an x-ray source which produces a fan-shaped x-ray beam penetrating the radiographic subject, the cross-sectional extent of which perpendicular to the layer plane is equal to the layer thickness and in the layer plane is of a magnitude such that the entire radiographic subject is penetrated, and also containing a radiation receiver which determines the intensity of radiation behind the subject, and also with a drive device for the measuring arrangement for producing rotary movements and with a measured value converter for transforming the signals supplied by the radiation receiver into a layer image, the radiation receiver being composed of a number of individual detectors.
In a known tomographic apparatus of this type, the radiation receiver comprises a single row of detectors and the measuring arrangement is rotated through an angle of 360.degree. to produce the input signals for the measured value converter. A tomographic apparatus of this type is suitable as a so-called entire-body scanner for photographing any desired transverse layer images. The detector row must be of such dimensions that the x-ray beam picked up by it fully permeates each body layer which is to be reproduced. The number of detectors should be determined in accordance with the largest body layer of which an image is to be made, and the image resolution required for this. In this instance, it is disadvantageous that when forming an image of a body layer which is substantially smaller than the maximum body layer, for example, a cross-section through the neck or the head of the patient, only a small number of detectors is operative for the production of the input signals for the measured value converter. The local resolution therefore decreases relative to the size of the body layer of which an image is to be formed.